Most of these agencies work isn't to spy ordinary citizens, they try to spy other agencies and governments so the USA can have the upper hand.
So spying on every single citizen is the best way to collect actual data
that matters? Have you watched the documentary Citizenfour? Obviously the NSA is exploiting their power and it just keeps growing.
I do not think that they would bother with every single Bitcoin user. However, I would not be surprised if they are monitoring it nor if they have agents among the community.
The IRS however has a huge interest in bitcoin. The only national laws that matters right now have to do with capitol gains. I would guess the IRS is looking into software to find out who is evading their tax liability.
At some point they may launch a campaign to get that money, plus fines. It won't effect people who are paying now, but could get ugly for anyone who has not. or they may do nothing. As an example look at internet purchases. When you buy something online you are supposed to keep track of it and pay taxes at the end of the year. Almost no one does that and it has gone on for years now with no legal action. It would now be impossible to go back through all the data and assess fines.
Even though NSA is spying on pretty much everything, Bitcoin and PGP are harder than their usual ways. I agree that the IRS is much more interested. This is why countries in which Bitcoin is tax exempt are much better than the US (e.g. Switzerland).
Bitcoin is tax exempt in the U.S. too. It's exchanging it for local fiat that causes the tax liability.